This invention relates to active optical devices, such as lasers, employing color centers and patterns thereof.
Recently there has been reported increasing interest in the properties of color centers in alkali halide crystals; and, in particular, a very transient type of phenomenon producing color centers by two-photon absorption has been reported. See the aticle by J. N. Bradford et al., Physical Review Letters, Volume 35, page 300 (1975).
The very short lifetime of the created color centers described in that work make them relevant only to the advancement of physical science, and not to practical devices.
Nevertheless, we have recognized that two-photon absorption for the production of color centers could be very useful because of the possibility of greater penetration depth into a material than has heretofore been realized in other radiation absorption processes involving color centers, and because there are no appropriate very short ultraviolet wavelength lasers, such as would be desired to create the stable color centers by single photon absorption. It is therefore an object of this invention to provide more practical, long-lived devices employing color centers generated by two-photon absorption.